PROJECT SUMMARY AND ABSTRACT: There is accumulating evidence that alterations in cerebral blood vessels contribute to brain dysfunction underlying Alzheimer's dementia (AD). Amyloid-beta is a major culprit in AD and has deleterious effects on neurons and glia. Amyloid-beta also profoundly alters the regulation of the cerebral microcirculation. However, little is known as to how amyloid-beta contributes to altering the neurovascular regulation. This issue is particularly important considering the fact that the brain is highly dependent on a ceaseless blood supply well matched to its metabolic needs. Therefore, the goal of this grant application is to investigate how amyloid beta alters the control mechanisms regulating the blood delivery to the brain and contributes to brain dysfunction. We have recently found that the tissue plasminogen activator (tPA), an enzyme best known for its involvement in vascular fibrinolysis, plays a key role in the mechanisms of neurovascular regulation via its ability to modulate a critical neuron-to-vasculature signaling pathway involving postsynaptic NMDA receptors (NMDAR), neuronal nitric oxide synthase (nNOS), and nitric oxide. Therefore, we will test the hypothesis that the reduction in tPA contributes to the neurovascular dysregulation and cognitive deficits induced by amyloid-beta in mice overexpressing the amyloid precursor protein. The central hypothesis will be tested in 3 specific aims: (1) reduced tPA activity contributes to the alteration in neurovascular regulation induced by amyloid-beta, (2) reduced tPA activity contributes to amyloid-beta-induced neurovascular dysregulation by impairing nNOS-derived nitric oxide production dependent on NMDA receptor, and (3) reduced tPA activity contributes to amyloid pathology and resulting cognitive deficits. These specific aims will be achieved by employing a multidisciplinary strategy combining in vitro molecular, biochemical, confocal and electron microscopic imaging, and in vivo physiological and behavioral approaches.